This invention relates to vehicle headlamp systems, and in particular to a system for automatically controlling the switching of the headlamps between the low beam and high beam settings.
Improved automotive control systems have freed drivers from performing a number of tasks that formerly required manual operations. Such systems relieve drivers from the distractions of these auxiliary systems and often result in improved concentration as well as reduced driver fatigue. One such system which has seen limited use is an automatic headlamp dimmer system for controlling the headlamps of a vehicle. In particular, an automatic headlamp dimmer system is designed to automatically dim the headlamps--i.e. switch from high beam to low beam--in the presence of lights from other vehicles. Since a vehicle's headlamps should be dimmed for both oncoming traffic as well as traffic being approached from behind, it is necessary for an automatic headlamp dimmer system to accurately sense both the presence of another vehicle's headlamps or taillamps.
While numerous automatic headlamp dimmer control systems have been developed, in general, these systems have had serious drawbacks due to poor performance, complexity or cost. These shortcomings, particularly in the area of performance, have been directly responsible for the limited use of automatic headlamp dimmer systems to date. Since these systems must sense light from headlamps as well as taillamps from other vehicles, a key performance requirement is the system's capability to distinguish this light from extraneous incoming light. Examples of such unwanted light include reflections from road signs, light from street lamps, or light from vehicles on other roadways. The problem of avoiding false responses to extraneous light signals is especially troublesome when it is considered that the intensity of these extraneous light signals can be many times greater than the intensity of the light signal from a taillamp. As a result, some prior art systems simply do not attempt to detect valid taillamp signals, but rather are designed to respond only to the light from oncoming headlamps which, of course, presents a much stronger signal. Other systems with sufficient sensitivity to detect the light from taillamps are susceptible to false triggering which degrades performance and leads to a lack of driver confidence in the system. As a result, users frequently disable the systems entirely and revert to manual control.
Spurious responses in automatic headlamp dimmer systems are also encountered in the presence of overhead flashing lights. Such flashing may be produced, for instance, by blinking overhead traffic lights, or by blinking construction lights or arrows. These flashes, when detected by conventional automatic headlamp dimmer sensors, can cause the system to undesirably cycle between high and low beams in synchronization with the flashing light. A similar situation is also encountered when windshield wipers are operated if the light sensor for the automatic headlamp dimmer system is positioned behind the windshield within the sweep of the wipers. Such placement is desirable because the sensor is not exposed to exterior debris, and further because the sensor's view is likely to be as unobstructed and clear as the driver's view. However, when the windshield wipers are operated, the sensor's field of view is periodically occluded by the wiper blade. This may cause the headlamp dimmer system (when in the low beam mode) to cycle to the high beam mode while the wiper is obstructing the view, and conversely to return back to the low beam mode when the wiper is not obstructing the sensor's field of view. Obviously, cycling of the automatic headlamp dimmer in response to flashing lights and windshield wiper activity is highly annoying and contributes to the low usage of such systems.
It is accordingly, a primary object of the present invention to provide an improved automatic headlamp dimmer system that is responsive to both the headlamps and taillamps of other vehicles, and yet is able to reliably distinguish between valid light signals and extraneous light signals.
It is another primary object of the present invention to provide an improved automatic headlamp dimmer system that is able to disregard blinking lights from stop lights and the like and thereby avoid spurious activation of the headlamp dimmer in response thereto. It is also an object of the present invention to provide an automatic headlamp dimmer system which has its light sensor mounted behind the windshield, with the sweep of the windshield wipers in its optical field of view, and yet which is non-responsive to the operation of the windshield wipers.
Generally, these objects are accomplished by providing a system that is sensitive to light only in the near infrared region, and which excludes other wavelengths including light in the visible region. More particularly, it has been determined that light from headlamps and taillamps contains a significant amount of signal information in the infrared region. On the other hand, light from extraneous light sources such as street lamps, reflections from road signs, etc., predominate in the visible region and contain very little signal information in the infrared band. Accordingly, by responding only to light in the near infrared region, the signal to noise ratio of the present system is greatly enhanced, thereby enabling the system to accurately recognize a taillamp signal in the presence of extraneous light signals several orders of magnitude greater in intensity.
Additionally, the automatic headlamp dimmer, according to the present invention, is able to detect the presence of a spurious periodically varying light signal and temporarily disable its switching capabilities to effectively ignore the spurious signal. In one embodiment of the present invention, the automatic headlamp dimmer system is provided with the capability of determining if periodic variations in the input light signal are characteristic of variations expected by operation of the vehicle's windshield wipers. If the received signal exhibits a predefined repetitive pattern, the system will respond by not allowing switching from low beam to high beam to occur during the time that the wipers block the field of view of the sensor.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings.